Of late, bristle articles such as brushes, brooms, paintbrushes, etc. have been increasingly made entirely from plastic. Numerous attempts have been made to replace the still conventional mechanical fixing of the bristles to the bristle carrier by thermal joining processes, in which on the bristle reception side of the bristle carrier and optionally the fixing end of the bristles are brought by melting into a soft plastic state and subsequently brought together under pressure action. In certain circumstances, it is sufficient to only zonely melt the bristle carrier at points where individual bristle bundles are to be fixed. On melting the bristle ends of a bristle bundle the plastic flows together to form a thickened portion, which simultaneously forms the basis for joining together the bristles. As a function of the material pair of the bristles and bristle carrier, a welded joint is obtained, i.e. an integral joint between the two materials, or a jointing connection, in which the bristles with their thickened end are surrounded by the soft plastic material of the bristle carrier and in this way are positively secured (DE-OS 34 03 341 which corresponds to U.S. Pat. No. 4,637,660).
The economics of this process is decisively dependant on the operating speed of the equipment used for it. Thus, it is known to bring a bristle endless strand up to the apparatus, cut off the bristle bundles with the desired length from the strand and after simultaneously heating the bristle carrier reception side and the bristle ends to bring same together and keep them in this state until, after adequately cooling, a firm joint has been made (DE-OS 34 03 343 and DE-OS 28 12 746). In this process the supply, cutting off, melting, joining and cooling take place at a single working station. The cycle time of an apparatus operating according to this process is naturally very long and in particular longer than in mechanical fixing processes, so that this only to a limited extent permits an economic manufacture of bristle articles.
It has therefore also been proposed (DE-OS 28 49 510) to provide on a turntable several holders reciprocately arranged with the same angular distances and which can in each case receive a plastic bristle carrier. In a first station the bristle carriers are fed from a magazine into a holder on the turntable. In the following station the bristle reception side of the bristle carrier is melted and simultaneously reception holes formed. At the third station the bristle bundles are supplied from the endless strand from the outside and all the bundles of a bristle occupancy or coverage are simultaneously supplied. The leading ends of the bristle bundles are melted in said station and subsequently pressed onto the bristle reception side of the bristle carrier. Following cooling adequate for transfer the bristle carrier with the mounted bristles passes into a further cooling station and then into a first further processing station, in which the bristles are cut to the final size and then into yet another further processing station in which the brush is cleaned and trimmed. Finally the finished brush passes into the position where it is discharged and a new bristle carrier supplied. In this process the longest cycle time occurs at the bristle supply station, where simultaneously the bristles and bristle carriers are melted and the two are brought together. There must subsequently be an adequate cooling time in order to achieve the hardening of the melt necessary for transfer. All the other working steps can in theory be performed more rapidly, but this is not possible due to the long cycle time at the supply and jointing station.
Much the same is the case in the aforementioned process (DE-OS 28 08 965), in which two turntables with parallel axes are juxtaposed, whereof one has in several positions holders for the bristle carriers and the other in several positions clamping devices for the bristle bundles. The turntable with the holders for the bristle carriers moves past a magazine from which in each use one bristle carrier is transferred into a holder. The holder then moves past a station with a heating device, where the bristle reception side is melted and simultaneously provided with reception holes. The bristle carrier then passes into a station, where the two turntables are in contact. The other turntable has at a first station a transfer mechanism, by means of which the already cut bristle bundles are removed from a magazine in a number corresponding to the occupancy or coverage and placed in the clamping device located on the turntable. In a second station the free bristle ends, which are used for fixing purposes are moved in front of a heating device, which melts the bristle ends thus joining them together. Finally the clamping device with the terminally melted bristle bundles pass into a common station, in which the bristles are transferred to the bristle carriers on the other turntable, pressed onto the bristle reception side and the bristles and bristle carriers are cooled until they can be transferred. The bristle carriers covered with the bristles are then moved into a discharge station. Compared with the previously mentioned process, a clock cycle reduction is obtained in that the melting of both the bristle carrier and the bristles takes place at an individual station of the two turntables, whereas only the bringing together and cooling are performed on the common station. However, this cycle time reduction is only insignificant, because the bringing together and jointing of bristles and bristle carriers, as well as the cooling necessary prior to transfer still lead to a long cycle time.
Apart from the aforementioned welding and jointing process, it has been known since the occurrence of plasticly deformable or molten-processable and finally foamable plastics, to produce the bristle carrier in moulds, dies, injection moulds or foaming moulds and in connection with said production to imbed the ends of the bristles in the plastic (U.S. Pat. Nos. 105,373, 654,184, 2,303,800, 3,408,112, 4,132,449, German Patent 845 933 and DE-AS 1 050 304). The bristles are introduced into one of the two mould parts of the single-split mould through reception openings until their ends project into the mould cavity and this is followed by moulding, injection moulding or foaming. After an adequate cooling or curing phase the finished bristle article is removed. However, the operating cycles are even longer than in the previously described welding and jointing processes due to the larger plastic quantity and therefore longer cooling time. In addition, as a result of the short clamping length of the linear bristles, they only have an inadequate resistance to tearing out. It has therefore already been proposed to initially melt the bristle ends and to shape them to a head (German Patent 845 933) or to shape all the bristle ends of a bristle coverage to a plate (DE-AS 10 50 304) and only then imbed same in the plastic of the bristle carrier. Although from the use standpoint this leads to better products, the cycle time is increased.
In order to speed up the cycle time, it is known (EP-OS 142 885 which corresponds to U.S. Pat. No. 4,685,313) to provide bristle holders in the form of a plurality of through holes in several index positions on a rotary table, in which the cut bristle bundles are inserted and finally made flush at their rear end, followed by melting at the fixing side end to a thickened portion and finally connected to one half of an injection mould, whose other half is to shape the planar bristle holders. Thus, in this case, the preparatory work on the bristles is carried out at several stations of a rotary table, the injection moulding in the injection mould taking place in the final station. However, even here there is a comparatively long cycle time due to the injection moulding and the cooling of the mould necessary for curing. The sealing of the bristle bundles or the reception holes with respect to the injection moulding material is also inadequate, because on the one hand the bristles cannot be sufficiently densely packed by merely inserting into the reception holes and on the other hand at the start of injection moulding, as a result of the pressure building up isostatically and which also acts behind the thickened portions on the bristle ends, the bristles are drawn into the mould and the thickened portions are raised from the mould-side opening edge of the reception holes. Therefore the injection moulding material penetrates between the bristles and between the latter and the wall of the hole. This leads to an unclean termination on the bristle carrier and the use-desired flexibility of the bristle bundles is unfavourably influenced and becomes non-uniform.
In another known process DE-OS 29 22 877) the reverse procedure is adopted, in that in each case one injection mould is positioned at several index positions on a rotary table and has in one mould part reception opening for the bristles. In the first index position the cut-to-size bristles are removed bundlewise from a magazine by means of cut-out tubes and subsequently inserted by the latter into the reception holes of the injection mould. At the same station injection moulding of the mould takes place and subsequently further rotation takes place into a cooling station. The further working of the bristles on the opened mould takes place in another station and finally the finished bristle article is removed from the mould. This process makes it possible to more significantly reduce the operating cycle, because injection moulding and cooling are distributed over different stations, but it is still unsuccessful as a result of the aforementioned problem of sealing the reception holes requiring special measures, particularly as the bristles are necessarily relatively loosely seated in said holes and also, as a result of the insertion of the bristles directly into the moulds, it is not possible for thickened portions to form on the bristle ends. Therefore injection moulding of the mould takes place in two stages, namely firstly part of the plastic is injected at a low pressure until the bristle ends are enveloped. Following the solidification of this melt, the remaining cavity space is filled in a second stage. This two-stage injection moulding with an intermediate cooling phase is technically complicated and timeconsuming.